Hydraulic system for trucks

ABSTRACT

A hydraulic system for simultaneously operating a plurality of attachments on a motor vehicle, such as a snow plow, dump body, or salt spreader. Separate valves for controlling the attachments are connected in parallel hydraulically between a common pressure manifold and a common return line so that the same pressure is available to each valve. In one embodiment a pressure compensated pump is connected between a fluid reservoir and the pressure manifold. The return line empties fluid into the reservoir. In another embodiment a pressure compensated main pump is connected between the common pressure manifold and the common return manifold to continually circulate fluid under pressure through the system while a priming pump initially charges the hydraulic system with fluid from the reservoir and thereafter maintains a pressurized flooded suction line on the main pump, and supplies make up hydraulic fluid to the system.

United States Patent 11 1 Veres [54] HYDRAULIC SYSTEM FOR TRUCKS [75] Inventor: Raymond M. Veres, Brooklyn, N.Y.

[73] Assignee: The Port of New York Authority,

New York, N.Y.

[22] Filed: July 21, 1971 [21] Appl. No.: 164,551

1111 3,733,818 1 51 May 22,1973

Primary Examiner-Edgar W. Geoghegan Attorney-Lee C. Robinson, Jr.

[ 5 7] ABSTRACT A hydraulic system for simultaneously operating a plurality of attachments on a motor vehicle, such as a snow plow, dump body, or salt spreader. Separate valves for controlling the attachments are connected [52] US. Cl ..60/422,60/97 P in parallel hydraulically between a common pressure [51] Int. Cl ..Fl5b 11/16 manifold and a common return line so that the same [58] Field of Search ..60/52 VS, 52 HE, pressure is available to each valve. In one embodiment 60/97 P a pressure compensated pump is connected between a fluid reservoir and the pressure manifold. The return [56] References Cited line empties fluid into the reservoir. In another embodiment a pressure compensated main pump is con- UNITED STATES PATENTS nected between the common pressure manifold and 2,223,838 12/1940 Tweedale ..60/52 vs UX the F manifmd minuauy circulate 2,643,515 6/1953 Harsch ..60/52 HE fluid under Pressure through the System While a P 2,892,3l2 6/1959 Allen et al ....60/52 HE ing pump initially charges the hydraulic system with 2,961,829 11/1960 Weisenbach ...60/53R fluid from the reservoir and thereafter maintains a 3,246,465 4/1966 Bookout et al. ..60/l9 pressurized flooded suction line on the main pump,

Stephens et al X and supplies make up hydraulic to the system 3,406,850 10/1968 Hancox ..60/52 HE X 8 Claims, 8 Drawing Figures I !:::I:l::::i:1:i:::1:l.

l T P I iii/2 5 i To PLOW LIFT I MOTOR a4 CYLINDER 1e 1 gfii' 6 I I I I HOIST I I CYLINDER A F B 44 v G a RESERVOIR PATENTEL 2 W3 SHEET 1 OF 7 NN W Dunn PATENIEI] HAYS? I973 SHEET 7 OF 7 OOON Ommam nIZDfi 002 89 00m 0 n 9 om on ow on 8 HYDRAULIC SYSTEM FOR TRUCKS BACKGROUND OF THE INVENTION The present invention relates to a system of simultaneously operating two or more hydraulic attachments for a vehicle, including such attachments as a snow.

plow, a dump body, or a salt spreader. In some prior systems of this type the attachment control valves are connected in series between an outlet manifold of the pump and a return line. The hydraulic fluid in such systems is continually circulated. When the valve of any one attachment is actuated the remaining valve downstream from it can not be actuated. Thus one disadvantage of such systems is that only one attachment may be operated at a time. Another disadvantage of such systems is that there is a pressure drop across each valve due to the valves restriction of the flow even when the valve is open. Thus at the valve furthest downstream from the outlet manifold of the pump the pressure available to operate the attachment is greatly reduced.

In series valve systems involving an attachment such as a salt spreader, the disadvantage of nonsimultaneousoperation can become significant. If the salt spreader must be stopped while the snow plow is raised or lowered, for example, the salt tends to cake and when the spreader is reactivated a non-uniform spread results.

In some other hydraulic control systems the valves to operate the various attachments are placed in parallel between a common pressure manifold and a common return line. In such systems the valves are normally closed and are opened to activate a particular attachment. When none of the attachments are being operated all the valves are closed and it is necessary to open a relief valve between the common pressure manifold and the common return line in order to relieve the fluid pressure built up by the pump. Generally such parallel valve systems use a spring compensated relief valve which opens at a predetermined pressure in excess of the normal operating pressure of the system to shunt excess fluid during periods of low flow demand.

One disadvantage of using only a pressure relief valve to compensate for periods of low flow demand by the system, such as when the valves for the attachments are all closed, is that the pump must do extra work to open the relief valve, to maintain it in an open position, and to keep the fluid circulating under pressure. This excess fluid flow through the relief valve also deteriorates the valve. This extra work manifests itself in the form of heat and also results in a waste of horsepower for the vehicle engine driving the pump.

Still another disadvantage of many such prior hydraulic control systems of both the series valve type and the parallel valve type is that the pumps commonly used do not adjust to the different flow rates required for different actuators. For example, the snow plow lift cylinder may only require 3 gallons per minute (g.p.m.) of hydraulic fluid to activate the cylinder at a given speed while the salt spreader mechanism may require as much as 30 gallons per minute of hydraulic fluid. The pumps used in many prior hydraulic control systems must be set for the highest rate which will be required which would be the total combined flow rate of all the attachments (assuming a parallel valve system). Flow restriction valves must then be used in supplying the attachments requiring a lower flow rate and the excess flow is channeled through the relief valve with a consequent waste of energy.

A disadvantage of some prior systems is due to the type of pump employed. In hydraulic systems using either vane or gear type pumps, the output flow rate is directly proportional to the pump speed. In order to have sufficient fluid output flow capacity to operate the hydraulic system at low pump speeds, large capacity pumps are utilized. The pump is commonly turned through a transmission system by the vehicle engine and thus the pump speed is a direct function of the vehicle engine speed. If the vehicle engine turns the large capacity pump at a high rate of speed the output flow rate produced is in excess of what is required by the system and there is consequent waste of horsepower as the excess fluid flow is by-passed through the relief valve. Thus in such prior systems there is often a very limited range of vehicle engine speed over which the pump may operate efficiently.

Still another disadvantage of many prior hydraulic systems on vehicles is that such systems often require the actuation of the valves by mechanical or hydraulic controls. Such systems are complicated and difficult to install on the vehicle.

These and other disadvantages are overcome by the novel design of the invention to be described hereinafter:

SUMMARY OF THE INVENTION A preferred embodiment of the present invention comprises a plurality of hydraulic actuators connected between a common pressure manifold and a common return manifold. A plurality of electro-magnetically op erated valves are interposed between each hydraulic actuator and the common pressure manifold. A pressure compensated pump supplies fluid from a fluid reservoir to the common pressure manifold at a predetermined pressure which is controlled to be substantially constant over a selected range of pump shaft speeds.

The hydraulic actuator valves are normally closed to prevent fluid from the common pressure manifold from reaching the hydraulic actuators. Upon the application of an electrical signal to a solenoid on a selected valve the valve is caused to open and allow pressurized fluid from the common pressure manifold to operate the hydraulic actuator. The valves are connected in parallel between the common pressure manifold and the common return line and therefore a plurality of valves may be opened at one time to simultaneously operate one or more actuators. The pump automatically adjusts to produce a flow rate just sufficient to maintain the predetermined pressure in the common pressure manifold as the flow rate requirement of the system varies with the opening or closing of one or more valves.

In one embodiment of the invention the common return line feeds directly into the reservoir and the pump draws only from the fluid reservoir. In another embodiment of the invention the pump is connected directly between the common pressure manifold and the common return line. An auxiliary pump is connected between the fluid reservoir and the common return line to initially pressure the system and to maintain the suction line of the main pump in a flooded, pressurized state. A fluid passage is provided between the common return line and a pressure relief valve which empties into the reservoir. When excess fluid builds up in the common pressure line, such as if the pressure compensator for the main pump malfunctions, the pressure relief valve opens to allow the excess fluid to be returned to the reservoir.

In contrast to series valve systems, since the main fluid stream does not have to pass through the valves when they are not being actuated, there is no pressure drop across each valve which would leave insufficient fluid pressure to be applied to the hydraulic actuator located furthest downstream from the pump.

Since the pump is self-compensating over a predetermined range of flow rates the pressure supplied to the common pressure manifold is maintained at a substantially constant predetermined value as the various hydraulic attachments are operated. Thus in one preferred embodiment while the plow lift cylinder (3 g.p.m. capacity) is being operated the pump supplies 3g.p.m. of hydraulic fluid at approximately 1200 lbs. per square inch (psi) to the common pressure manifold. If the spreader mechanism (30 gpm. capacity) is thereafter simultaneously actuated, the pump automatically adjusts its output flow rate to supply the additional 30 gallons per minute at the 1200 psi predetermined pressure for a total output flow rate of 33 g.p.m.

In one preferred embodiment a check valve is connected between the dump body hoist cylinder feed line and the common return line. The check valve is opened for fluid passage by means of fluid pressure being applied through a safety line connected to the common pressure manifold. When the check valve is open any fluid inadvertently applied to the dump body hoist cylinder is routed to the common return line to effectively short circuit hydraulically the dump body hoist cylinder, rendering it inoperable. The purpose of this safeguard is to prevent the dump body hoist cylinder from being operated when the salt or sand spreader mechanism is mounted in the dump body during winter operation of the vehicle. The safety line is connected at the same time that the spreader mechanism is installed in the dump body.

It is therefore an object of the present invention to provide a hydraulic system for selectively operating two or more attachments on a motor vehicle simultaneously.

It is a further object of the invention to provide a hydraulic system for operating attachments mounted on a vehicle wherein a source of fluid is maintained under a substantially constant pressure for the sequential or simultaneous application to two or more of the attachments.

Still another object of the invention is to provide a hydraulic system for operating attachments on a motor vehicle including a snow plow, a dump body hoist, and a salt or sand spreader wherein any one of the attachments may be operated singly or simultaneously with the other attachments and wherein a safety mechanism is provided for rendering inoperable the dump body attachment when the spreader attachment is connected to the system.

The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodiments of the invention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view ofa truck equipped with one embodiment of the invention;

FIG. 2 is an enlarged view of the plow attachment of the truck of FIG. 1;

FIG. 3A and 38 together constitute a schematic diagram of one embodiment of the invention;

FIG. 4 is a sectional view of the fluid pump of the embodiment in FIGS. 3A and 3B;

FIG. 5 is a schematic diagram of a portion of a second embodiment of the invention;

FIG. 6A illustrates the pump output flow rate characteristic as a function of the pump speed for a typical vane or gear type pump; and

FIG. 63 illustrates the pump output flow rate characteristic as a function of the pump speed of the pump of the embodiment of FIGS. 3A and 33.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Referring now more particularly to FIGS. 1 and 2 a truck 10 is shown with a dump body attachment 12 and a plow attachment 14. As shown more clearly in FIG. 2 the plow blade assembly 14 is lifted by a hoist cylinder 16 which moves a lever arm 18. The lever arm 18 is pivotally mounted at one end on a rigid frame 20 mounted on the front of the truck. A chain 22 is connected between the free end of the lever arm 18 and the plow blade assembly 14.

The plow blade assembly 14 is angled in a horizontal plane by a hydraulic transverse motor 24 mounted on a V-shaped horizontal extension 26 of the frame 20. The motor 24 is reversible and drives a worm gear 28 which engages a semicircular segment gear 30 attached to the plow blade assembly 14. The plow blade assembly 14 is mounted on the extension 26 of the frame 20 in such a manner that it may be pivoted by the motor 24 to approximately 35 left or right from the straight bulldozing angle. The motor-gear assembly 24, 28, and 30 is designed to have a sufficient gear-reduction ratio that it will automatically hold the plow blade assembly in any selected position of angle irrespective of the snowload or of the speed of the vehicle when plowing.

A pressure compensated hydraulic pump 32 is mounted on the front of the truck 10. The pump is driven through a reduction gear 34 (shown diagrammatically in FIG. 3A) from the truck engine. The output port of the pump 32 is connected to a common pressure manifold 36. The suction line 38 of the pump is connected to a hydraulic fluid reservoir 40 mounted on the right hand side of the truck just back of the cab.

Referring now to FIGS. 3A and 38, a common return line 42 is connected between the hydraulic fluid reservoir 40 and the hydraulic attachments to be described hereinafter. The output flow of the pump 32 is controlled by a pressure compensator 44 mounted on the pump 32 as will be described in greater detail hereinafter. The pump 32 is connected by still another line 46 to the fluid reservoir for purposes of cooling the pump during operationQ As stated above, the hydraulic pump 32 is of the pressure compensated type. Such pumps are known in the art and have been described in various patents such as U.S. Pat. Nos. 2,776,627, 2,776,628 and 2,776,629. It is to be understood that while the embodiments to be described utilize pumps of this type other types of pressure compensated pumps may be used in other embodiments.

Referring now to FIG. 4 the operation of the pump 32 will be briefly described. The pump has a main drive shaft 48 bearing mounted at both ends in a casing 50. A generally circular, wobble or swash plate 52 is pivotally mounted in the casing 50 in such a manner that it may be rotated about an axis perpendicular to the axis of rotation of the shaft 48. The shaft 48 passes through the center of the plate 52.

A cylinder barrel 53 is attached to the shaft 48 so as to rotate with the shaft. The cylinder barrel contains a plurality of pumping pistons 54 slidable in separate bores 55 arranged radially about the rotational axis of the cylinder barrel 53. The bores 55 in which the pistons 54 slide are connected at one end alternately as the cylinder barrel rotates past a valve plate (not shown) to the inlet and outlet ports of the pump. The ends of the pistons are connected by ball joints to the inclined plate 52.

In operation as the shaft 48 and cylinder barrel 53 rotate the plate 52 is held in a fixed angular position relative to the axis of rotation of the shaft and cylinder barrel 53 and so it acts as an eccentric cam to reciprocate the pistons 54 in their bores 55. The angular position of the plate 52 is automatically adjusted by a pressure compensator 44 including a compensating piston 56 which presses against the plate 52 through a ball joint 58. The force of the pressure compensating piston 56 is restrained by anadjustable return spring 60 pressing against the plate through similar ball joint in the opposite direction. 7

The fluid pressure at the pump outlet normally increaseswhen the speed of the pump is increased or when the number of attachments in operation is decreased. The pressure compensator 44, including the return spring 60, is adjusted such that when the increasing fluid pressure at the pump outlet starts to exceed a predetermined pressure (selected to be 1200 psi) the compensating piston 56 pushes against the plate 52 to adjust it to a more perpendicular position with respect to the shaft 48 and cylinder barrel 53 thus reducing the degree of eccentricity of the plate with respect to the pumping pistons 54. The angular position of the plate is adjusted by an amount just sufficient to maintain the fluid pressure at the pump outlet at the predetermined pressure. In the extreme case, if the plate 52 is completely perpendicular to the shaft 48, the pistons 54 are not reciprocated at all but remain relatively stationary in their bores 55 to produce substantially no fluid output flow from the pump. As the plate 52 is moved toward the perpendicular position the horsepower required to drive the pump decreases.

When the fluid pressure at the pump outlet falls to 50 psi below the predetermined pressure, such as occurs when an additional attachment is put into operation or the pump speed is decreased, the pressure compensator 44 causes the compensating piston 56 to return the plate 52 to its maximum driving position.

Referring now to FIG. 6A, in a conventional vane or gear type pump the output flow rate of the pump is directly proportional to the speed of the pump shaft. Even when the maximum required output flow for the hydraulic system is exceeded the pump continues to increase its flow rate and the excess flow (designated 61 in FIG. 6A) must be diverted through a pressure relief valve. This diverted extra fluid flow represents a waste of horsepower for the vehicle engine driving the pump and also results in an increase in the heat generated within the system.

This disadvantage is obviated by the pressure compensated pump 32 of the present embodiment. The purpose of the pump compensator control 44 is to au tomatically adjust pump delivery to meet the system's need. The output flow rate characteristic of the pump 32 is illustrated in FIG. 6B when all of the attachments are in operation and the maximum pump output flow is required. In the case of the preferred embodiment the maximum pump output flowis 45 g.p.m. at 1800 rpm of the pump shaft 48. Further increases in the pump speed, as for example when the vehicle engine is being operated at high speed, does not result in an increase in input horsepower to the pump. The plate 52 is adjusted, as described above, to maintain the pump output at 45 g.p.m. and 1200 psi.

Referring again more particularly to FIGS. 3A and 3B, connected between the common pressure manifold 36 and the common return line 42 are a plurality of electromagnetically operated hydraulic valves for controlling the attachments on the truck 10. The valves are normally closed so that no fluid may flow through them but they may be selectively actuated to make one or more fluid connections to the common pressure manifold and to the common return line to feed pressurized hydraulic fluid to predetermined attachments.

A valve 62 is connected by a line 64 to the common pressure manifold 36 and by a line 66 to the common return line 42. A flow restriction valve 68 is interposed in the line 64 to adjust the amount of fluid flow passing through the line. The output side of the valve 62 is connected by two lines 70 and 72 to the plow traverse motor 24. Two electrically operated solenoids 74 and 76 are mounted on opposite sides of the valve 62 to control its operation. When solenoid 74 is energized a spool within the valve is moved to connect line 64 to line 70 and to connect line 66 to line 72. This allows fluid at 1200 psi to flow from the common pressure manifold and pass through the plow traverse motor, causing the plow to be angled in the desired direction, and to circulate back to the common return line 42.

When the solenoid 74 is de-energized the valve automatically shuts off leaving the plow locked in whatever position it was in when the solenoid 74 was deenergized. When the solenoid 76 is energized the valve spool is moved so that line 70 is connected to line 66 and line 72 is connected to line 64. Fluid at 1200 psi is thereafter applied through line 72 to the plow traverse motor 24 to turn the plow blade in the opposite direction until the solenoid 76 is de-energized, at which time the plow remains set in some new position.

The solenoids 74 and 76 are controlled by a selfcancelling, rocker type switch 78 mounted on a control panel 80 in the truck cab. The switch 78 is of the type which normally does not connect either solenoid to the truck power supply but when pushed at its upper end, as viewed in FIG. 3B, it connects the truck power sup ply to energize the solenoid 74 and when pushed at its lower end, as viewed in FIG. 3B, it connects the truck power supply to energize the solenoid 76.

A valve 81 is connected by a line 82 to the common pressure manifold and by a line 84 to the common return line. A single line 86 connects the output side of the valve 81 to the plow lift cylinder 16. A flow restriction valve 88 is interposed in the line 86 to regulate the fluid flow rate to and from the cylinder 16. The valve 81 is equipped with two electromagnetically operated solenoids and 92. The solenoids 90 and 92 are operated by a self-cancelling, rocker type switch 94 mounted on the control panel 80. When the switch 94 is pushed at its lower end, as viewed in FIG. 3B, it energizes the solenoid 90 to operate the valve 80 to connect line 86 with line 82. This allows fluid from the common pressure manifold to flow into the plow lift cylinder 16 to raise the plow assembly 14. To lower the plow, the switch 94 is pushed at its upper end, as viewed in FIG. 33, to activate the solenoid 92 and operate the valve 81 to connect line 86 to the line 84. This allows the fluid previously injected into the cylinder 16 to be relieved through the line 84 to the common return line 42.

The dump body hoist 12 is controlled by a valve 96. The valve 96 is connected by a line 98 to the common pressure manifold 36 and by a line 100 to the common return line 42. The output side of the valve 96 is connected by a line 102 to a hydraulic cylinder (not shown) for operating the dump body 12. A flow restriction valve 104 is interposed in the line 102 to control the rate of fluid flow to and from the dump body hoist cylinder. The valve 96 is equipped with two solenoids 106 and 108 which are operated by a rocker type, selfcancelling switch 110 mounted on the control panel 80. When the switch 110 is pushed at its lower end, as viewed in FIG. 3B, the solenoid 106 operates the valve to connect line 102 with line 98 thereby allowing pressurized fluid to flood the dump body hoist cylinder and raise the dump body 12. When the upper end of the switch 110 is pushed the solenoid 108 is energized to operate the valve 96 so as to connect line 102 with line 100, thereby relieving the dump body hoist cylinder of its fluid and lowering the dump body.

The line 102 is also connected by a line 112 through a check valve 114 to the common return line 42. The check valve 114 is connected by a line 116 through a snap coupling 118 to the common pressure manifold 36. If the coupling 118 is open so that the line 116 is not connected to the common pressure manifold, the check valve 114 will be closed and no fluid can pass from the line 112 to the common return line. With this condition of the valve 114 the dump body hoist may be operated. The coupling 118 is snapped together at the same time the spreader mechanism 120 is installed in the back of the truck dump body. When the coupling 118 is made to connect the line 116 to the common pressure manifold the check valve 114 is opened and any fluid applied to the dump body hoist cylinder through line 102 is directly routed to the common return line through the line 112 and the valve 114. This prevents the dump body hoist from being operated when the spreader mechanism 120 is installed in the dump body.

The spreader mechanism 120 is connected to the common pressure manifold through a line 122 and a snap coupling 124 and is connected to the common return line through a line 126 and a snap coupling 128. The spreader mechanism 120 is of a known type, having an agitator motor 130 for mixing the slat or sand which is to be spread, a conveyor motor 132 for conveying the material to the spinner, and a spinner motor 134 for spraying the sand or salt on the road bed. The motors 130, 132, and 134 are connected in common to the return line 126.

The motors 130 and 132 are connected through separate portions of an electrically controlled spreader valve 136 to the pressure line 122. The 134 135 is likewise connected through a separate portion of the electrically controlled valve 136 to the pressure line 122. interposed between the snap coupling 124 and the valve 136 is a solenoid operated valve 138. When the solenoid operated valve 138 is energized through a switch 140 on the control panel 80 to pass fluid to the valve 136 the spreader mechanism 120, as a whole, is operated. The flow rate of pressurized fluid delivered to the motors 130 and 132 is varied by a servo mechanism within the valve 136 which is linked to a selector switch 142 mounted on a control panel 80. The flow rate of pressurized fluid delivered to the spinner motor 134 is varied by a servo mechanism within the valve 136 which is linked to a selector switch 144 mounted on the control panel 80.

A pressure relief valve 146 is connected to the common pressure manifold by a line 148 and to the common return line by a line 150. The pressure relief valve 146 is adjusted to connect line 148 with line 150 when the pressure across the valve 146 reaches approximately 1500 psi. The relief valve 146 is intended for emergency use in the even that one of the various other valves or the pump malfunctions and excessive pressure is built up in the common pressure manifold 36.

An additional line 152 connects the valve 146 and the line 148 to a solenoid operated return valve 154. The output side of the valve 154 is connected by a line 156 to the line 150 and thus to the common return line 42. The valve 154 is normally open, thereby connecting line 152 with line 156. This has the effect of providing a free fluid connection between the common pressure manifold 36 and the common return line 42 so that the output of pump 32 is diverted through the valves 146 and 154 to the common return line 42.

This shunting effects minimizes the amount of work which must be done to turn the pump during times when the attachments are not being operated. When any one of the various hydraulically operated attachments is activated a signal is passed from the control panel 80 to energize a solenoid 158 mounted on the valve 154 to close the valve thereby diverting the pressurized fluid to the attachment control valves. During the operation of any one of the attachments fluid does not normally flow through the valves 146 and 154 and they are effectively blocked out of the system. It is only when none of the attachments are being operated that fluid passes through the valves 146 and 154 to the common return manifold.

Referring now more particularly to FIG. 5 a second embodiment of the invention is shown comprising substantially the same system as disclosed in the embodiment of FIGS. 3A and 33 with the exception of the pump system and the omission of the return valve 154 and its associated lines 156 and 152. The hydraulic system of the embodiment of FIGS. 3A and 38 may be described as an open loop hydraulic system. By open loop is meant that the suction line 38 of the main pump 32 is connected to a fluid reservoir rather than connected to the return line 42.

In contrast to the open loop system the embodiment of FIG. 5 may be described as a closed loop hydraulic system wherein the suction line of a pressure compensated primary pump 160 is connected directly to the common return line 42. When the truck engine turns the pump 160 through the reduction gear 34 fluid is drawn directly from the common return line 42 by the pump 160 and is pumped under pressure into the common pressure manifold 36.

The pump 160 is similar in construction to the pump 32. In has a swash plate pivotally mounted in the pump casing which may be angled by a pressure compensating piston to vary the output flow of the pump as explained above in reference to pump 32. A flow restriction valve 162 is interposed between the output line 164 of the pump 160 and the common pressure manifold 36. The flow restriction valve 162 is adjusted to allow a fixed rate of flow (approximately 45 g.p.m.) of hydraulic fluid to the system. The pump 160 is adjusted to supply fluid at a maximum pressure of 1200 psi to the common pressure manifold.

The hydraulic system is initially charged with fluid by an auxiliary pump 166 connected by a line 168 to the fluid reservoir 40 and by a line 170 to the common return manifold 42. Although the auxiliary pump 166 is shown in FIG. as being separate from the primary pump 160 the two pumps are actually manufactured as one unit. A filter 172 and a hand operated valve 174 are interposed in series hydraulically in the line 168. the pump 166 additionally maintains a pressurized, flooded suction line to the pump 160 during normal operation. Thus when a demand is made on the system for a high flow rate, such as by operating the spreader 120, additional fluid is pumped into the system by the auxiliary pump 166. Hydraulic fluid for cooling the pump 160 returns through a line 182 to the reservoir 40.

When the demand ceases the excess fluid is emptied back into the reservoir 40 through the line 170. A pressure relief valve 176 is connected in series hydraulically to a filter 178 and a hand operated valve 180. The pressure relief valve 176 is adjusted to open at a pressure in excess of 100 psi. When none of the valves 62, 81, 96 and 138 are open to operate the attachments, the pump 160 dead-heads against the common pressure manifold and it is adjusted by its pressure compensating mechanism to supply a minimum flow rate at the predetermined pressure of 1200 psi. In contrast to the open loop system of FIGS. 3A and 3B the closed loop" system of FIG. 5 maintains the predetermined pressure in the common pressure manifold even when no attachment is being operated.

It should be apparent that while the above embodiments of the invention have been described in reference to a truck equipped with a dump body, a plow and a material spreader the hydraulic control system of the invention could be used to control a plurality of any type of hydraulic attachments on vehicles other than trucks. For example a system according to the invention could provide for simultaneous control of the hydraulic attachments of a four-wheeled farm tractor.

The terms and expressions which have been employed here are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possicommunication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold at a predetermined pressure, the pump means including means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the pump means to maintain the pressure of the fluid in the common pressure manifold substantially constant at the predetermined pressure over a predetermined range of output flow rates of the pump means, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between each of the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, electromagnetic means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a hydraulically operated safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.

2. A hydraulic system as recited in claim 1 wherein at least two of the valves within the valve means are connected in parallel hydraulically between the common pressure manifold and the common return line.

3. A hydraulic system as recited in claim 2 wherein the pump means comprises a casing having an inlet port and an outlet port, a shaft, means for rotatably mounting the shaft in the casing about an axis, a cylinder barrel mounted on the shaft, the cylinder barrel having a plurality of radially spaced, axially extending bores, pistons reciprocable in the bores, means for alternately connecting the bores to the inlet and outlet ports in timed relationship to the rotation of the cylinder barrel, a plate pivotally mounted in the casing for rotation about an axis substantially perpendicular to the axis of rotation of the shaft, the plate being in driving relationship with the pistons, and means responsive to fluid pressure at the outlet port for varying the pitch of the plate relative to the shaft in direct relationship to changes in the fluid pressure.

4. A hydraulic system as recited in claim 1 wherein the valve means comprises means for providing free fluid communication between the common pressure manifold and the common return line at times when the valve means is not directing fluid to the hydraulic actuators.

5. A hydraulic system for use on a motor driven vehicle to operate a plurality of hydraulic actuators, comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold at a predetermined pressure, the pump means including a primary pump connected between the common pressure manifold and the common return line, means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the primary pump to maintain the pressure of the fluid in the common pressure manifold substantially constant at the predetermined pressure over a predetermined range of output flow rates of the pump means, and an auxiliary pump connected between the fluid reservoir and the common return line for initially charging the system with fluid and for maintaining a pressurized flow of fluid to the primary pump, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between each of the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, electromagnetic means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a hydraulically operated safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.

6. A hydraulic system for operating a plurality of hydraulic actuators, the system comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the safeguard valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.

7. A hydraulic system for operating a plurality of hydraulic actuators, the system comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold, the pump means including means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the pump means to maintain the pressure of the fluid in the commonpressure manifold within a predetermined range, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected in parallel between the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the safeguard valve is open, removable fluid connection means between the safeguard valve and the common pressure manifold, and means for selectively removing the connection means to prevent the opening of the safeguard valve.

8. A hydraulic system as recited in claim 1 wherein the opening of the safeguard valve prevents operation of the of the selected hydraulic actuator. 

1. A hydraulic system for use on a motor driven vehicle to operate a plurality of hydraulic actuators, comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold at a predetermined pressure, the pump means including means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the pump means to maintain the pressure of the fluid in the common pressure manifold substantially constant at the predetermined pressure over a predetermined range of output flow rates of the pump means, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between each of the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, electromagnetic means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a hydraulically operated safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.
 2. A hydraulic system as recited in claim 1 wherein at least two of the valves within the valve means are connected in parallel hydraulically between the common pressure manifold and the common return line.
 3. A hydraulic system as recited in claim 2 wherein the pump means comprises a casing having an inlet port and an outlet port, a shaft, means for rotatably mounting the shaft in the casing about an axis, a cylinder barrel mounted on the shaft, the cylinder barrel having a plurality of radially spaced, axially extending bores, pistons reciprocable in the bores, means for alternately connecting the bores to the inlet and outlet ports in timed relationship to the rotation of the cylinder barrel, a plate pivotally mounted in the casing for rotation about an axis substantially perpendicular to the axis of rotation of the shaft, the plate being in driving relationship with the pistons, and means responsive to fluid pressure at the outlet port for varying the pitch of the plate relative to the shaft in direct relationship to changes in the fluid pressure.
 4. A hydraulic system as recited in claim 1 wherein the valve means comprises means for providing free fluid communication between the common pressure manifold and the common return line at times when the valve means is not directing fluid to the hydraulic actuators.
 5. A hydraulic system for use on a motor driven vehicle to operate a plurality of hydraulic actuators, comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold at a predetermined pressure, the pump means including a primary pump connected between the common pressure manifold and the common return line, means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the primary pump to maintain the pressure of the fluid in the common pressure manifold substantially constant at the predetermined pressure over a predetermined range of output flow rates of the pump means, and an auxiliary pump connected between the fluid reservoir and the common return line for initially chArging the system with fluid and for maintaining a pressurized flow of fluid to the primary pump, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between each of the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, electromagnetic means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a hydraulically operated safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.
 6. A hydraulic system for operating a plurality of hydraulic actuators, the system comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected between the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the safeguard valve is open, and means for selectively opening the safeguard valve by providing a removable fluid connection between the safeguard valve and the common pressure manifold.
 7. A hydraulic system for operating a plurality of hydraulic actuators, the system comprising a reservoir of fluid, a common pressure manifold, a common return line, means for providing fluid communication between the common return line and the reservoir, pump means for supplying fluid from the reservoir to the common pressure manifold, the pump means including means responsive to the pressure of the fluid in the common pressure manifold for adjusting the output flow rate of the pump means to maintain the pressure of the fluid in the common pressure manifold within a predetermined range, valve means for selectively controlling the hydraulic actuators, the valve means including a plurality of valves connected in parallel between the hydraulic actuators and the common pressure manifold, each of the valves being normally closed to the passage of fluid to each actuator, means for selectively opening each valve to provide fluid communication between one or more selected actuators and the common pressure manifold, a safeguard valve connected between a selected hydraulic actuator and the common return line so as to shunt pressurized fluid applied to the selected actuator to the common return line when the safeguard valve is open, removable fluid connection means between the safeguard valve and the common pressure manifold, and means for selectively removing the connection means to prevent the opening of the safeguard valve.
 8. A hydraulic system as recited in claim 1 wherein the opening of the safeguard valve prevents operation of the of the selected hydraulic actuator. 